Spread and impacts of non-native Caragana arborescens, an emergent invasive shrub in the prairie region

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Invasive non-native plant species are one of the biggest threats to biodiversity and ecosystems functioning. This is particularly true for invasive trees and shrubs, which have the potential to transform entire ecosystems. In Canada, 150 non-native trees and shrub species have been introduced and planted, many of which were imported before regulatory risk assessments. The invasiveness of these legacy species has never been systematically assessed. The non-native Caragana arborescens is a legume shrub that has been widely planted as shelterbelts and ornamental hedges in the prairie provinces. An increasing number of observations has shown that the species is escaping into nearby natural habitat, including in protected areas. Given its biological traits, Caragana arborescens could become an ecosystem transformer. However, there is little information on its extent of spread, the factors that favor its invasion, and its impacts on native ecosystems.By using Caragana arborescence as a study species, our project will (1) develop an approach to assess the invasiveness and ecosystem impacts of widely planted non-native trees and shrubs in the prairie provinces and (2) create evidence-based knowledge to help policy makers and land managers assess new guidelines on the management of legacy trees and shrubs. Specifically, our outcomes will assist provincial governments in evaluating the necessity of placing Caragana arborescence on provincial noxious weed lists and to consider methods to pro-actively control escaping stands and save costs to taxpayers in the long-term.